Noise control constitutes a rapidly growing economic and public policy concern for the construction industry. Areas with high acoustical isolation (commonly referred to as ‘soundproofed’) are requested and required for a variety of purposes. Apartments, condominiums, hotels, schools and hospitals all require walls, ceilings and floors that are specifically designed to reduce the transmission of sound in order to minimize or eliminate the disruption to people in adjacent rooms. Soundproofing is particularly important in buildings adjacent to public transportation including highways, airports and railroad lines. Additionally, theaters and home theaters, music practice rooms, recording studios and others require increased noise abatement for acceptable listening levels. Likewise, hospitals and general healthcare facilities have begun to recognize acoustical comfort as an important part of a patient's recovery time. One measure of the severity of multi-party residential and commercial noise control issues is the widespread emergence of model building codes and design guidelines that specify minimum Sound Transmission Class (STC) ratings for specific wall structures within a building. Another measure is the broad emergence of litigation between homeowners and builders over the issue of unacceptable noise levels. To the detriment of the U.S. economy, both problems have resulted in major builders refusing to build homes, condominiums and apartments in certain municipalities; and in cancellation of liability insurance for builders.
When a problem arises and the project success is at risk, the building owner must remediate the existing constructed building partitions. Various construction techniques and products have emerged to address the problem of noise control, but few are well suited to a situation of post-construction remediation. Choices include: additional gypsum drywall layers; the addition of resilient channels plus additional isolated drywall panels; and the addition of mass-loaded vinyl barriers plus additional drywall panels; cellulose-based sound board. All of these changes incrementally help reduce the noise transmission, but not to such an extent that identified problems areas would be considered fully mitigated (restoring privacy or comfort). The noise may come from rooms above or below the occupied space, or from an outdoor noise source. In fact, several of the above named methods only offer a two to eight decibel improvement in acoustical performance over that of standard construction techniques that have no regard for acoustical isolation. Such a small improvement represents a just noticeable difference, not a soundproofing solution. A popular example solution is that of an additional layer of gypsum wallboard added to an existing wall assembly. This addition only improves the wall's acoustical performance by two to three decibels overall. Such a difference would not be perceptible under normal living conditions. To be truly effective (yielding an improvement in acoustical performance of ten decibels or more), one side of the wall is typically demolished and reconstructed with additional soundproofing measures and materials. This traditional approach involves the burden of additional, costly construction materials, or extra labor expense due to complicated designs and additional assembly steps, and oftentimes, both expensive materials and labor.
More recently, an alternative building noise control product having laminated structures and utilizing a viscoelastic glue has been introduced to the market. The foregoing structures are disclosed and claimed in U.S. Pat. No. 7,181,891 issued Feb. 27, 2007 to the assignee of the present application. The contents of this patent are incorporated by reference herein in its entirety. Laminated structures disclosed and claimed in the '891 Patent include gypsum board layers and these laminated panels eliminate the need for additional materials such as resilient channels, mass loaded vinyl barriers, and additional layers of drywall during initial construction. The resulting system offers excellent acoustical performance improvements of up to 15 decibels in some cases. However, these structures are better suited for new construction than for the acoustical remediation of existing walls or other building partitions. A first shortcoming of this solution is the cost of the premanufactured panel. Such panels consist of five to 11 layers of materials carefully laminated in prescribed manufacturing method. As a result, the panels typically cost significantly more than traditional drywall panels of the same general dimensions. Further, such panels cannot be cut using the traditional tools used in the drywall installation trades. Rather than using a box cutter or utility knife to score the panel for fracture by hand, the panels must be scored multiple times and broken with great force over the edge of a table or workbench. Often times, the quality of the resulting break (in terms of accuracy of placement and overall straightness) is poor. In practice, skilled trades typically resort to the use of power tools such as saws and rotary cutters. This adds to the dust generation, the time required to install the panels, and the time required for site cleanup.
An alternative to the premanufactured panels mentioned above is that of the field application of a viscoelastic glue to regular drywall panels. In this method of noise control, the tradesperson or building owner purchases standard gypsum drywall and a quantity of viscoelastic glue, packaged in buckets or caulking tubes. The tradesperson then distributes the glue via a caulk gun or trowels it across the surface of an unmounted sheet of drywall. After the glue is allowed to dry, the installer tilts the coated drywall sheet onto an existing wall assembly. Viscoelastic glues of the type described here are available from Serious Materials of Sunnyvale, Calif. and Green Glue Company of Fargo, N. Dak. The foregoing method of self assembly has the opportunity to effectively mitigate noise, but is has many obvious shortcomings. First, for a typical architectural installation, the glue must be spread across many hundreds, if not thousands of square feet of gypsum panels. This requires an expansive and inconvenient lay down area for such an activity. Second, the spreading of so much glue in a controlled manner requires considerable effort and labor expense. It is not typical for the drywall trades to spread glue and manually create such assemblies. Special crews need to be trained in the method and many refuse to take on this additional responsibility. Those who do perform the task may pass on exceptional labor charges for the task to the owner of general contractor. In many cases, the installed cost of the final assembly is greater than that of the premanufactured panels. Another shortcoming of this method is the inconsistent assembly technique. The performance of the assembly is very dependent upon the quality of the glue application (including glue layer thickness and coverage). With individual field application of the critical glue component, one can not guarantee the final performance of a given assembly. Many of these assemblies underperform the glue manufacturers' expectations by five to 20 decibels.
Accordingly, what is needed is a new material and a new method of construction to reduce the transmission of sound from a given room to an adjacent area while simultaneously minimizing the materials required and the cost of installation labor during construction.